1. Field of the Invention
The present invention relates to combine harvesters having stone traps for collecting stones and other foreign objects before they reach the threshing means of the harvesters and enabling the trapped stones to be easily removed from the harvesters.
2. Description of the Prior Art
When harvesting windrow crops with a pick-up attachment mounted on a header of a combine harvester, or when cutting the crops close to the ground surface with a direct-cut attachment, stones and other hard foreign objects are frequently picked-up and fed into the harvester. To avoid damage caused by stones, combine harvesters commonly have trough-shaped stone traps disposed forwardly of the threshing means. Stones which are fed towards the threshing means are hit by threshing bars of the threshing means and thereby thrown into the trap.
However, small trough-shaped stone traps are not fully adequate for retarding all stones which are likely to cause damage. Larger stone traps may be fully adequate for retarding the stones, but may also adversely influence the fluent transition of crop material from a crop elevator of the harvester to the threshing means. This decreases the efficiency of the harvester.
One attempted solution according to U.S. Pat. No. 3,209,759 has been to provide a feeder beater above a large stone retarder. However, this results in higher cost of the harvester. Moreover, the header, together with the crop elevator, have to be mounted further to the front to accomodate the feeder beater. This reduces the fore-and-aft stability of the harvester.
Another attempted solution according to U.S. Pat. No. 2,652,677 is to provide a transition plate between the crop elevator and the threshing means. The transition plate is held in an operative position relative to the threshing means by spring biased latches but, in response to a pre-determined abnormal pressure, is released and undergoes pivotal movement. However, the adjustment of traps having such transition plates has proved very difficult and the operator must be alert to determine when the trap opens.